Memory cells

ABSTRACT

Some embodiments include memory cells. A memory cell may contain a switching region and an ion source region between a pair of electrodes. The switching region may be configured to reversibly retain a conductive bridge, with the memory cell being in a low resistive state when the conductive bridge is retained within the switching region and being in a high resistive state when the conductive bridge is not within the switching region. The memory cell may contain an ordered framework extending across the switching region to orient the conductive bridge within the switching region, with the framework remaining within the switching region in both the high resistive and low resistive states of the memory cell.

TECHNICAL FIELD

Memory cells.

BACKGROUND

Memory is one type of integrated circuitry, and is used in computersystems for storing data. Integrated memory is usually fabricated in oneor more arrays of individual memory cells. The memory cells areconfigured to retain or store memory in at least two differentselectable states. In a binary system, the states are considered aseither a “0” or a “1”. In other systems, at least some individual memorycells may be configured to store more than two levels or states ofinformation.

An example memory device is a programmable metallization cell (PMC).Such may be alternatively referred to as a conductive bridging RAM(CBRAM), nanobridge memory, or electrolyte memory. A PMC may use ionconductive material (for instance, a suitable chalcogenide or any ofvarious suitable oxides) sandwiched between a pair of current conductiveelectrodes, and such material may be referred to as “switching”material. A suitable voltage applied across the electrodes can generatecurrent-conductive super-ionic clusters or conducting filaments. Suchmay result from ion transport through the ion conductive material whichgrows the clusters/filaments from one of the electrodes (the cathode)and through the ion conductive material. The clusters or filamentscreate current-conductive paths between the electrodes. An oppositevoltage applied across the electrodes essentially reverses the processand thus removes the conductive paths. A PMC thus comprises a highresistance state (corresponding to the state lacking a conductive bridgeextending through a switching material) and a low resistance state(corresponding to the state having a conductive bridge extending througha switching material), with such states being reversibly interchangeablewith one another.

Although there has been some effort toward development of PMC devices,there remains a need for improved memory cells. Accordingly, it would bedesirable to develop new memory cells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 diagrammatically illustrates an example embodiment PMC reversiblytransitioning between a low resistance state and a high resistance statethrough application of appropriate electrical fields across the memorycell.

FIGS. 2 and 3 diagrammatically illustrate an example embodiment PMC.FIG. 2 is a cross-sectional side view of the PMC, and FIG. 3 is a viewalong the line 3-3 of FIG. 2.

FIGS. 4 and 5 diagrammatically illustrate another example embodimentPMC. FIG. 4 is a cross-sectional side view of the PMC, and FIG. 5 is aview along the line 5-5 of FIG. 4.

FIG. 6 is a diagrammatic expanded view of a region “A” of FIG. 5, andillustrates an example configuration of a pattern extending across suchregion.

FIG. 7 is another diagrammatic expanded view of the region “A” of FIG.5, and illustrates another example configuration of a pattern extendingacross such region.

FIGS. 8-10 diagrammatically illustrate another example embodiment PMC.FIG. 8 is a cross-sectional side view of the PMC, FIG. 9 is a view alongthe line 9-9 of FIG. 8, and FIG. 10 is a view along the line 10-10 ofFIG. 8. An example conductive bridge is shown in FIG. 10, but not shownin either of FIGS. 8 and 9.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

PMC devices (for instance, CBRAM devices) may utilize interstitialdiffusion/drift of metal cations (for instance, Ag⁺, Cu⁺, etc.) alongwith electrochemical redox to reversibly form conductive filaments, andto thereby reversibly switch the devices between a high resistance stateand a low resistance state. The conductive filaments may form within anelectrolyte. In conventional PMC devices, an amorphous glass may serveas a solid electrolyte. The amorphous glass may comprise, for example,an oxide or chalcogenide.

The region of the PMC that supports the conductive filaments switchesfrom low resistance in the presence of the conductive filament to highresistance in the absence of the conductive filament, and may bereferred to as a “switching region.”

A difficulty encountered with conventional PMC devices is that there maybe non-uniformity of programming characteristics across an array of thedevices. Such non-uniformity may result, at least in part, fromrandomness in the formation of conductive filaments within individualPMC devices. Specifically, each conductive filament results fromdendritic growth of conductive material across the switching region,analogous to Brownian motion diffusion through the amorphous electrolytenetwork within the switching region. The random variability associatedwith such stochastic process leads to cell-to-cell non-uniformity inprogramming behavior, which problematically limits performance of memoryarrays utilizing PMC devices.

In some embodiments, the invention includes incorporation of an orderedframework within a switching region of a PMC device, with such frameworkbeing configured to confine conductive filaments as they are formedacross the switching region, and to thereby reduce the problematicvariability associated with dendritic growth in conventional PMCdevices.

FIG. 1 shows a PMC device 10 in a high resistance state (II) and a lowresistance state (L). The two resistance states are reversiblyinterchanged with one another through application of electric fields EF⁺and EF⁻, with EF⁺ being of opposite polarity relative to EF⁻.

The PMC device comprises a pair of electrodes 12 and 14; and comprises aswitching region 16 and an ion source region 18 between the electrodes.

Electrodes 12 and 14 may comprise any suitable electrically conductivecomposition or combination of compositions; and may be the samecomposition as one another or may be different compositions relative toone another.

The memory cell 10 is shown to have the bottom electrode 12 connected toexternal circuitry 30, and to have the top electrode 14 connected toexternal circuitry 32. Circuitries 30 and 32 may correspond to senseand/or access lines coupled to the electrodes, and configured forproviding the appropriate electric fields across the memory cell duringread/write operations. In some embodiments, the illustrated memory cellmay be one of a plurality of memory cells of a memory array, and thecircuitries 30 and 32 may be utilized to uniquely address each of thememory cells. In some embodiments, a “select device” (not shown) may beprovided adjacent the memory cell to reduce undesired current leakage toand/or from the memory cell during utilization of the memory cell in amemory array. Example select devices include diodes, transistors, ovonicthreshold switches, etc.

The ion source region 18 contributes ions which ultimately formconductive bridges across the switching region 16. The ion source regionmay comprise any suitable composition or combination of compositions;and in some embodiments will comprise one or both of copper and silver,and thus be configured for contributing copper cations and/or silvercations for formation of a conductive bridge. For instance, the ionsource region may comprise a combination of copper and tellurium. Theion source region is shown to be electrically conductive, andspecifically is shown with hatching analogous to the hatching utilizedfor illustrating the electrically conductive electrodes 12 and 14.

The switching region 16 may be a solid, gel, or any other suitablephase, and may comprise chalcogenide-type materials (for instance,materials comprising germanium in combination with one or more ofantimony, tellurium, sulfur and selenium), oxides (for instance,zirconium oxide, hafnium oxide, tungsten oxide, silicon oxide, etc.)and/or any other suitable materials.

The switching region is shown to comprise pathways 25 (diagrammaticallyillustrated with dashed-lines) that extend across the switching region,and specifically that extend from electrode 12 to ion source region 18.The pathways may be considered to be part of an ordered framework withinthe switching region which is configured to orient a conductive bridgeas the bridge forms across the switching region. The pathways arepresent in both the high resistance state (H) and the low resistancestate (L) of the memory cell 10, but in the low resistance state aplurality of particles 24 (for instance, atoms or atomic clusters)extend along one of the pathways to form a conductive bridge 26extending across the switching region 16. The individual particles maybe charged or neutral along the conductive bridge. For instance, in someembodiments the individual particles may be ionic clusters and/or may beindividual ions; and in some embodiments the individual particles may beelectrochemically-plated metal. Although the conductive bridge is shownto comprise a plurality of particles, in some embodiments the particlesmay merge so that the conductive bridge is a single continuous filament.The conductive material within the conductive bridge may be any suitablecomposition or combination of compositions, and in some embodiments maycomprise, consist essentially of, or consist of one or both of copperand silver.

The conductive bridge 26 is shown formed along one of the pathways 25,and conductive particles 24 are shown to deposit along a couple of theother pathways to create partial bridges. In some embodiments,conductive bridges may start along numerous pathways, but once a bridgeis completed along one of the pathways current will pass along suchbridge and the growth of bridges along the other pathways in the memorycell will cease.

Although multiple conductive pathways are shown extending through theswitching region of the illustrated cell 10, in other embodiments (notshown) there may be only a single pathway provided across such switchingregion.

In the shown embodiment, the application of electric field EF⁺(specifically a field oriented from the shown top electrode to the shownbottom electrode) causes growth of the conductive bridge 26, and thustransitions the memory cell from the high resistance state (H) to thelow resistance state (L); and the application of electric field EF⁻dissipates the conductive bridge 26, and thus transitions the memorycell from the low resistance state (L) to the high resistance state (H).The ordered framework remains within the switching region 16 in both thehigh resistance and the low resistive states of the memory cell, andaccordingly the pathways 25 are shown to extend across the switchingregion in both states of the memory cell. The pathways 25 confineconductive bridges 26 to specific locations within a switching region,and thus provide for more ordered growth of the conductive bridges thanoccurs in conventional PMC devices. Such ordered growth may improvedevice-to-device uniformity during programming across a memory array.Thus, PMC devices having the pathways 25 may be utilized to developmemory arrays having improved performance relative to memory arrayscomprising conventional PMC devices.

The ordered framework within the switching region may comprise anysuitable composition or combination of compositions; and in someembodiments may comprise, consist essentially of, or consist of one ormore of GeS, GeSe, SiO, ZrO, TiO, TaO, HfO, AlO, WO, SnO, NbO, ZrTiO,ZrWO, AlTiO, VO, MoO, NiO, YO, ReO, MnO, FeO, SiAlO, SiTiO; where thelisted compositions are described in terms of principle components,rather than in terms of specific stoichiometries (for instance, AlO maycorrespond to Al₂O₃).

In some embodiments, it may be desired to chemically modify the materialof the switching region to enhance formation and/or orientation of thepathways. Such modification may be accomplished utilizing, for example,one or more of ion exchange with cationic surfactant, thermal diffusion,photo-diffusion, etc.

In some embodiments, the pathways 25 may correspond to tubularstructures (for instance, cylindrical micelles) extending through theswitching region, or may correspond to interfaces along lamellar sheets.FIGS. 2-7 illustrate example embodiments in which the pathwayscorrespond to tubular structures, and FIGS. 8-10 illustrate exampleembodiments in which the pathways correspond to interfaces alonglamellar sheets.

Referring to FIGS. 2 and 3, an example embodiment memory cell 10 acomprises the electrodes 12 and 14 discussed above, and comprises theswitching region 16 and ion source region 18. The illustrated switchingregion comprises tubular structures 40 (only some of which are labeled)extending through a matrix 42. The tubular structures define thepathways 25 discussed above with reference to FIG. 1.

The tubular structures may be formed within the matrix utilizing anysuitable processing, including, for example, emulsion templating, blockcopolymer technologies which form surface-normal cylinders, and/ormethodologies which form tubular mesostructures. Example methodologiesare described in MacLachlan et al. “Non-Aqueous Supramolecular Assemblyof Mesostructured Metal Germanium Sulphides from [Ge₄SIO]⁴⁻ Clusters”Nature 397 (1999) 681-4; Scott et al. “Synthesis of Metal SulfideMaterials with Controlled Architecture” Current Opinion Sol State & MatSci 4 (1999) 113-121; MacLachlan et al. “Mesostructured Metal GermaniumSulfides.” J. Am. Chem. Soc. 121 (1999) 12005-12017; Templin et al.“Organically Modified Aluminosilicate Mesostructures from BlockCopolymer Phases” Science 278 (1997) 1795-8; Imhof et al. “OrderedMacroporous Materials by Emulsion Templating” Nature 389 (1997) 48-51;Holland et al. “Synthesis of Macroporous Minerals with Highly OrderedThree-Dimensional Arrays of Spheroidal Voids” Science 281 (1998) 538-40;Kresge et al. “Ordered Mesoporous Molecular Sieves Synthesized by aLiquid-Crystal Template Mechanism” Nature 359 (1992) 710; Beck et al. “ANew Family of Mesoporous Molecular Sieves Prepared with Liquid CrystalTemplates” J Am. Chem. Soc. 114 (1992), 10834; and Trikalitis et al.“Supramolecular Assembly of Hexagonal Mesostructured Germanium Sulfideand Selenide Nanocomposites Incorporating the Biologically RelevantFe₄S₄ Cluster.” Angew. Chem. Int. Ed. 39 (2000) 4558-62.

The tubes 40 may be considered to be a confinement system; withindividual tubes being configured to confine material of a conductivebridge. Specifically, the tubes may be configured to have internaldiameters suitable for retaining and confining the material of aconductive bridge (for instance, the particles 24 of FIG. 1). In someembodiments, the tubes may have internal cross-sectional widthdimensions of less than or equal to about 30 Å; and in particularembodiments may have internal cross-sectional width dimensions of fromabout 10 Å to about 20 Å. Such tubes may be particularly suitable forretaining copper-containing particles and/or silver-containing particleshaving thicknesses of less than or equal to about 20 atoms; such as, forexample, particles having thicknesses of at least about 1 atom and lessthan or equal to about 20 atoms. In some embodiments, the particles mayhave thicknesses within a range of from about 5 atoms to about 20 atoms.

The tubular structures 40 may be utilized to confine conductiveparticles (for instance, the particles 24 of FIG. 1) along a verticalpath through the switching region during formation of a conductivebridge (for instance, the bridge 26 of FIG. 1). The particulararchitectures of the conductive bridges may depend on, among otherthings, the interior dimensions of the tubes; the charge, size andcomposition of the particles; and the composition and charge along thewalls of the tubes. For instance, the conductive bridges may compriseparticles stacked one directly over the other as shown in the embodimentof FIG. 1, or may comprise particles that spiral along an interior wallof a tube. Regardless, the conductive bridges are confined within thetubes and form a vertical interconnect that extends through theswitching region.

Although the tubes are shown to be circular in cross-section, in otherembodiments the tubes may have other shapes, and may be, for example,elliptical or polygonal in cross-sectional shape (for instance, thetubes may be hexagonal as discussed below with reference to FIGS. 5-7).

The illustrated cell 10 a has a vertical dimension 43 and a lateraldimension 45 orthogonal to the vertical dimension. It can be preferredthat the tubes have interior diameters which are substantially smallerthan the lateral dimension of the switching region to achieve desiredconfinement of conductive bridging material. In some embodiments, thetubes may have maximum interior cross-sectional width dimensions whichare less than or equal to about 20 percent of the lateral dimension ofthe switching region.

The tubular structures 40 may be representative of tubularmesostructures (i.e., tubular units) formed by various methods analogousto the methods described in the references listed above. In someembodiments, the tubes may correspond to hexagonal units comprising oneor more of GeS, GeSe, SiO, ZrO, TiO, TaO, HfO, AlO, WO, SnO, NbO, ZrTiO,ZrWO, AlTiO, VO, MoO, NiO, YO, ReO, MnO, FeO, SiAlO, SiTiO; where thelisted compositions are described in terms of principle components,rather than in terms of specific stoichiometries. For instance, thetubes may correspond to hexagonal units comprising germanium and one orboth of sulfur and selenium.

FIGS. 4-7 illustrate an example memory cell 10 b analogous to the cell10 a of FIGS. 2 and 3, and comprising hexagonal units 46 (only some ofwhich are labeled) extending through the switching region 16. Thehexagonal units may be formed with any suitable processing, including,for example, various methods analogous to the methods described in thereferences listed above. Thus, in some embodiments the hexagonal unitsmay comprise germanium in combination with one or both of selenium andsulfur.

The illustrated hexagonal units have a maximum cross-sectional dimension47. In some embodiments, such dimension may be less than or equal toabout 30 Å; and may be, for example, from about 10 Å to about 20 Å.

FIGS. 6 and 7 show an enlarged view of some of the hexagonal units ofFIG. 5, and illustrate a couple different embodiments of such hexagonalunits. FIG. 6 shows that the hexagonal units 46 (only some of which arelabeled) may be formed around core materials 48 (only some of which arelabeled). More generally considered, the tubes 46 may be formed aroundorganic material that is within the interior regions of the tubes.

In some embodiments, the hexagonal units may consist of inorganicsubstances, and the core materials may comprise organic substances. Forinstance, the hexagonal units may comprise negatively charged clustersof Ge₄Q₁₀, (where “Q” corresponds to one or both of sulfur andselenium), and the core material may comprise one or more surfactantcounterions. Such configurations may be formed by, for example,processes analogous to those described in Trikalitis et al. andMacLachlan et al.

The conductive particles utilized to form a conductive bridge (forinstance, the particles 24 of FIG. 1) may pack into the interiors of thehexagonal units together with the surfactant counterions to form theconductive bridge (analogous to the bridge 26 discussed above withreference to FIG. 1) extending through the switching region 16 (FIG. 4).The composition and charge of the surfactant may be tailored to modifythe rate at which the particles pack into the interiors of the hexagonalunits, and may thereby be utilized to tailor programming characteristicsof a PMC device.

FIG. 7 shows an embodiment in which there is no organic material withinthe interior regions of the hexagonal units. In some embodiments, thestructure of FIG. 7 may correspond to a processing stage subsequent tothat of FIG. 6. Specifically, the organic material of FIG. 6 may beremoved (for instance, by ashing, calcination, and/or solvent exchangeextraction) to leave a construction in which only the inorganic walls ofthe hexagonal units remain. In some embodiments, it may be advantageousto remove the organic material in order to improve thermal stability ofa PMC device. For instance, if the organic material is present, the PMCdevice may be stable to only about 400° C. (due to thermal degradationof the organic material), whereas the device may be thermally stable totemperatures above 400° C. if the organic material is not present.

The embodiments of FIGS. 2-7 utilize tubular pathways to confineparticles during formation of conductive bridges across switchingregions. In other embodiments, the pathways may be planar pathwaysextending across the switching regions, rather than tubular pathways. Aplanar pathway may confine a conductive bridge along a verticaldirection through a switching region, but may allow freedom along ahorizontal direction. Thus, the planar pathways provide more confinementof the conductive bridges than is achieved with conventional PMC devices(which essentially have no framework for confining conductive bridgesthrough a switching region), but provide less confinement than isachieved with the tubes of the embodiments of FIGS. 2-7. In someembodiments, it may be advantageous to utilize planar pathways in thatit may be more economical to fabricate such pathways than to fabricatetubular pathways, and the control of conductive bridge architectureprovided by the planar pathways may be sufficient to achieve desireduniformity of programming characteristics across a memory array.

FIGS. 8-10 illustrate an example memory cell 10 c analogous to the cell10 of FIG. 1, and comprising planar pathways 50 (only some of which arelabeled) extending through the switching region 16. In some embodiments,the pathways 50 may correspond to interfaces along alternating lamellarsheets 51 and 53. The lamellar sheets 51 and 53 differ in compositionrelative to one another, and may be formed in the desired alternatingarrangement with any suitable processing. For instance, an upper surfaceof electrode 12 may be appropriately treated to induce self-assembly ofdiblock material or other material which forms alternating lamellarsheets. Alternatively, one of the sheets 51 and 53 may consist ofinorganic material and the other may comprise organic material (such as,for example, surfactant). After the lamellar sheets are formed in thedesired configuration, the organic material may be removed, if sodesired.

The device 10 c of FIG. 8 may be considered to have a vertical axisthrough the switching region 16 which is parallel to the planes of theinterfaces 50. Such device will have horizontal axes orthogonal to suchvertical axis. The cross-section of FIG. 9 has a dashed-line axis 52provided therein to diagrammatically illustrate that there is freedomalong a horizontal axis for the growth of the conductive bridges(analogous to the bridge 26 shown in FIG. 1). FIG. 10 shows a view alongone of the interfaces 50, and shows a conductive bridge 26 formed alongsuch interface. The bridge extends vertically along the interface, buthas freedom along a horizontal axis 52 so that the bridge is tippedrelative to a vertical axis 54 through the switching region. Incontrast, if vertical tubes analogous to the tubes of FIGS. 2-7 areutilized instead of the vertical planes, the conductive bridge could beconfined along the vertical direction of axis 54.

The electronic devices discussed above may be incorporated intoelectronic systems. Such electronic systems may be used in, for example,memory modules, device drivers, power modules, communication modems,processor modules, and application-specific modules, and may includemultilayer, multichip modules. The electronic systems may be any of abroad range of systems, such as, for example, clocks, televisions, cellphones, personal computers, automobiles, industrial control systems,aircraft, etc.

The particular orientation of the various embodiments in the drawings isfor illustrative purposes only, and the embodiments may be rotatedrelative to the shown orientations in some applications. The descriptionprovided herein, and the claims that follow, pertain to any structuresthat have the described relationships between various features,regardless of whether the structures are in the particular orientationof the drawings, or are rotated relative to such orientation.

The cross-sectional views of the accompanying illustrations showfeatures within the planes of the cross-sections, and generally do notshow materials behind the planes of the cross-sections in order tosimplify the drawings.

When a structure is referred to above as being “on” or “against” anotherstructure, it can be directly on the other structure or interveningstructures may also be present. In contrast, when a structure isreferred to as being “directly on” or “directly against” anotherstructure, there are no intervening structures present. When a structureis referred to as being “connected” or “coupled” to another structure,it can be directly connected or coupled to the other structure, orintervening structures may be present. In contrast, when a structure isreferred to as being “directly connected” or “directly coupled” toanother structure, there are no intervening structures present.

In some embodiments, a memory cell comprises a switching region and anion source region between a pair of electrodes. The switching region isconfigured to reversibly retain a conductive bridge. The memory cell isin a low resistive state when the conductive bridge is retained withinthe switching region and is in a high resistive state when theconductive bridge is not within the switching region. An orderedframework extends across the switching region to orient the conductivebridge within the switching region. The framework remains within theswitching region in both the high resistive and low resistive states ofthe memory cell.

In some embodiments, a memory cell comprises a switching region and anion source region between a pair of electrodes. The switching region isconfigured to reversibly retain a conductive bridge. The memory cell isin a low resistive state when the conductive bridge is retained withinthe switching region and is in a high resistive state when theconductive bridge is not within the switching region. A confinementsystem is within the switching region and is configured to confinematerial of the conductive bridge along one or more pathways through theswitching region. The confinement system remains within the switchingregion in both the high resistive and low resistive states of the memorycell.

In some embodiments, a memory cell comprises a switching region directlyagainst a first electrode, and comprises an ion source region directlyagainst the switching region. The ion source region comprises one orboth of copper and silver. The switching region has a vertical dimensionbetween the first electrode and the ion source region, and has a lateraldimension orthogonal to the vertical dimension. The memory cell alsocomprises a second electrode directly against the ion source region. Theswitching region comprises an ordered electrically insulative frameworkwhich is configured to orient materials from the ion source regionduring formation of a conductive bridge of the materials across theswitching region. The framework comprises at least one hexagonal tubehaving a maximum interior cross-sectional width dimension of less thanor equal to about 20% of the lateral dimension of the switching region.

In compliance with the statute, the subject matter disclosed herein hasbeen described in language more or less specific as to structural andmethodical features. It is to be understood, however, that the claimsare not limited to the specific features shown and described, since themeans herein disclosed comprise example embodiments. The claims are thusto be afforded full scope as literally worded, and to be appropriatelyinterpreted in accordance with the doctrine of equivalents.

I claim:
 1. A memory cell, comprising: a switching region and an ionsource region between a pair of electrodes; the switching region beingconfigured to reversibly retain a conductive bridge; the memory cellbeing in a low resistive state when the conductive bridge is retainedwithin the switching region and being in a high resistive state when theconductive bridge is not within the switching region; a confinementsystem within the switching region and configured to confine material ofthe conductive bridge along one or more pathways through the switchingregion; the confinement system remaining within the switching region inboth the high resistive and low resistive states of the memory cell; andwherein the confinement system comprises a structure that orients atleast one of the pathways along a vertical direction through theswitching region while allowing freedom along a horizontal direction. 2.A memory cell, comprising: a switching region and an ion source regionbetween a pair of electrodes; the switching region being configured toreversibly retain a conductive bridge; the memory cell being in a lowresistive state when the conductive bridge is retained within theswitching region and being in a high resistive state when the conductivebridge is not within the switching region; a confinement system withinthe switching region and configured to confine material of theconductive bridge along one or more pathways through the switchingregion; the confinement system remaining within the switching region inboth the high resistive and low resistive states of the memory cell; andwherein the confinement system comprises a hexagonal unit extendingthrough the switching region.
 3. A memory cell, comprising: a switchingregion and an ion source region between a pair of electrodes; theswitching region being configured to reversibly retain a conductivebridge; the memory cell being in a low resistive state when theconductive bridge is retained within the switching region and being in ahigh resistive state when the conductive bridge is not within theswitching region; a confinement system within the switching region andconfigured to confine material of the conductive bridge along one ormore pathways through the switching region; the confinement systemremaining within the switching region in both the high resistive and lowresistive states of the memory cell; and wherein the confinement systemcomprises a charged hexagonal unit comprising germanium and one or bothof sulfur and selenium; and wherein such charged hexagonal unitsurrounds at least one surfactant counterion.
 4. A memory cell,comprising: a switching region and an ion source region between a pairof electrodes; the switching region being configured to reversiblyretain a conductive bridge; the memory cell being in a low resistivestate when the conductive bridge is retained within the switching regionand being in a high resistive state when the conductive bridge is notwithin the switching region; a confinement system within the switchingregion and configured to confine material of the conductive bridge alongone or more pathways through the switching region; the confinementsystem remaining within the switching region in both the high resistiveand low resistive states of the memory cell; and wherein the confinementsystem comprises lamellar sheets extending substantially verticallyacross the switching region from one of the electrodes to the ion sourceregion.